Scanning system having a deflectable probe tip

Abstract

The invention is directed to a scanning system having one or several deflectable probe tips which are excited to oscillation at or near their resonant frequency. A saturation amplifier ( 16 ) is provided for detecting and measuring the phase shift between the excitation signal and the oscillation carried out by the probe tip. The saturation amplifier ( 16 ) generates a rectangular signal from the incoming sinusoidally-shaped signal ( 3 e ) while exactly maintaining the time-dependent position of the zero crossovers of the signal. The detection system, which is required for each probe tip, thereby acquires a very simple configuration of few commercially available components. Saturation amplified rectangular signals exclusively form the basis for the further evaluation. For this reason, a substantial independence of the signal intensity of the oscillation signal is ensured.

What is claimed is:  
     
       1. A scanning system comprising: 
       at least one deflectable probe unit;  
       said probe unit including: a deflectable probe tip having a resonance frequency; and, an actuator operatively connected to said probe tip to impart oscillatory movement thereto;  
       an oscillator for supplying an output excitation signal to said actuator for exciting said probe tip to oscillate at or near said resonance frequency;  
       said probe unit further including a sensor detecting the oscillation of said probe tip and outputting a sensor signal indicative of said oscillation;  
       a detection loop for determining the phase difference between said output excitation signal applied to said actuator and said sensor signal; and,  
       said detection loop including a saturation amplifier for receiving and operating on said sensor signal.  
     
     
       2. The scanning system of  claim 1 , said sensor signal having zero crossovers; and, said saturation amplifier being configured to produce a rectangular output signal (A) from said sensor signal while maintaining the zero crossovers of said sensor signal. 
     
     
       3. The scanning system of  claim 2 , further comprising a multiplier connected downstream of said saturation amplifier; said oscillator supplying a reference signal (Ref 1 ) to said multiplier; and, said multiplier multiplying said output signal (A) of said saturation amplifier by said reference signal (Ref 1 ) of said oscillator. 
     
     
       4. The scanning system of  claim 3 , further comprising a lowpass filter connected downstream of said multiplier. 
     
     
       5. The scanning system of  claim 4 , further comprising a phase-shifting circuit for shifting said reference signal (Ref 1 ) of said oscillator in phase. 
     
     
       6. The scanning system of  claim 5 , said phase-shifting circuit being an RC member having a variable resistor for shifting the phase of said reference signal (Ref 1 ). 
     
     
       7. The scanning system of  claim 4 , said saturation amplifier being a first saturation amplifier and said reference signal being a first reference signal (Ref 1 ) and said multiplier being a first multiplier and said lowpass filter being a first lowpass filter; and, said scanning system further comprising: a second saturation amplifier; said oscillator supplying a second reference signal (Ref 2 ) to said second saturation amplifier shifted in phase by 90° relative to said first reference signal (Ref 1 ); a second multiplier connected downstream of said second saturation amplifier; and, a second lowpass filter connected downstream of said second multiplier. 
     
     
       8. The scanning system of  claim 3 , further comprising a control arrangement for adjusting said deflectable probe tip to a pregiven fixed value of the phase difference between said output excitation signal of said oscillator and said sensor signal. 
     
     
       9. The scanning system of  claim 1 , wherein the operating frequency of said oscillator is variable. 
     
     
       10. The scanning system of  claim 1 , wherein said scanning system comprises a plurality of said deflectable probe units and a plurality of said detection loops for corresponding ones of said deflectable probe units and each of said detection loops including a saturation amplifier.